1. Field of the Invention
The present invention relates in general to a system and a method for reducing plasma induced communication disruption, and in particular to a system and a method for reducing plasma induced communication disruption utilizing electrophilic injectant and sharp reentry vehicle nose shaping.
2. Description of the Related Art
Blazing fiery descent of space-borne objects into Earth atmosphere is a well known phenomenon. To avoid damage or destruction during the fiery reentry phase, reentry vehicles are usually equipped with heat-shields known as the thermal protection system (TPS). With a TPS shield, it is the outer layer of TPS, rather than the structure of the reentry vehicle, that is subject to the intense heat and pressures during reentry. However, the thermal protection system itself is not indestructible. For instance, the outer layer of TPS ablates away under the extreme heat and pressures of reentry phase. As the TPS chars and partly burns away, a layer of plasma is created around the reentry vehicle from the ablation process.
Plasma is a state of matter in which molecules or atoms are broken down to free electrons and positively charged ions—atoms with electrons stripped away—under extreme heat. The TPS ablation releases certain easily ionizable trace elements in the TPS—mainly the low ionization potential alkali metals such as Na, K, and Ca—into a thin layer of flow around the reentry vehicle. A significant portion of these atoms ionize when they are subject to the high temperatures that exist in the thin boundary layer of flow around the reentry vehicle. Equal numbers of singly ionized positive ions (Na+, Ca+, and K+) and free electrons (e−) are generated, and an overall charge balance is maintained. Although these trace elements are usually present only at very low levels in the TPS material, on the order of tens of parts per million, they make a large contribution to the free electron concentration in the vehicle boundary layer.
Another source of plasma is from ionization of the air molecules, primarily in the region of the nose tip shock wave. In this region just at the front of the vehicle, the bow shock wave is at right angles to the flow and produces much higher temperatures than exist in the flow along the sides of the vehicle. Immediately behind this right-angle shock wave, the air is highly dissociated and partially ionized to a mixture of N, O, NO, N2, O2, NO+, and e− molecules and ions. The most easily ionizable air derived specie is NO, making creation of NO+ the principle source of “clean air” ionization free electrons. While not present in ambient air in significant amounts, NO is formed rapidly when the air is dissociated by the high temperatures at the nose tip. The relatively intense plasma formed at the nose tip flows back along the vehicle sides and eventually around the back into the wake, thinning as it goes and mixing with the boundary layer flow with its alkali metal produced ions. Hence, there are two major plasma contributors, one from the nose tip bow shock and the other from the ablating TPS layer with its alkali trace elements.
One result of plasma formation around a reentry vehicle is communication disruption during reentry. The free electrons racing around in the plasma interfere with the electromagnetic waves used for radio communication (the RF signals), resulting in communication disruption. The communication blackouts of space capsules or space shuttles that occur during their reentry into Earth atmosphere are caused by this plasma effect.
The plasma effect also adversely affects the targeting accuracy of reentry vehicles of the ICBM systems. One method of assuring the accuracy of the missiles is to guide the reentry vehicles utilizing the GPS system. However, the same plasma effect disrupts the vehicles' communication with the GPS satellites, causing so-called GPS blackouts during reentry. Because the reentry vehicles cannot be guided by GPS during the critical reentry phase, the targeting accuracy is negatively affected by the plasma induced communication disruption.
The technology for reducing or suppressing plasma effect, thus, would provide numerous benefits, including making space flights safer and making missiles more accurate. It can be seen, then, there is a need in the field for a system and a method for reducing plasma induced communication disruption during reentry.